A novel fluorescent malondialdehyde-lysine adduct

We report a novel type of fluorescent product derived from the reaction of the lysine residue with malondialdehyde (MDA). When the lysine-containing peptide (N-acetyl-glycyl-L-lysine methyl ester) was treated with MDA prepared by the acid hydrolysis of 1,1,3,3-tetramethoxypropane, the main fluorescent product, which corresponded neither to the 1-amino-3-iminopropene derivative (2) nor to the 4-methyl-1,4-dihydro-3,5-dicarbaldehyde derivative (3), was detected by reverse-phase HPLC. By analysis of its UV, NMR, and high-resolution FAB mass spectra, it was confirmed to be 1-[5-carboxymethyl-5-(N-acetylglycylamino)pentyl]-3-[1-(5-carboxymethyl-5-(N-acetylglycylamino)-pentyl)-3,5-diformyl-1,4-dihydropyridin-4-yl]pyridinium (1). This finding may provide a new clue to the formation mechanisms of fluorescent lipofuscin-like pigment.